The present invention relates to an apparatus of coating electro-photographic sensitive members, a method of coating electro-photographic sensitive members by said apparatus, and electro-photographic sensitive members prepared by said coating method, and particularly, in manufacturing of electro-photographic sensitive members, to a coating apparatus of forming an organic photo-sensitive layer on the outer surface of a cylindrical base member, a coating method of using said coating apparatus, and electro-photographic photo-sensitive member.
Conventionally, inorganic compounds such as selenium, cadmium sulfide, and zinc oxide and organic compounds such as polyvinyl carbazole have been proposed as photo-conductive materials constituting a photosensitive layer on an electro-photographic sensitive member. For multi-layer electro-photographic sensitive members each of which has a photosensitive layer, a charge generation layer, and a charge transfer layer, various organic compounds have been proposed as charge generating materials and charge transferring materials and have been actually used for organic photo-sensitive members. Conventionally, these organic photo-sensitive members have been made by various coating methods such as dipping, spraying, spinning, beading, wire-bar, blade, roller, extrusion, and curtain methods. Particularly, the dipping coating method has been widely used to form uniform photo-sensitive layers on the outer surface of a cylindrical base member.
Recently, demands have been increasing to make apparatus using an electro-photographic photo-sensitive member such as duplicating machines, printing machines, facsimile machines smaller and less weighted. To meet the demands, the electro-photographic photo-sensitive members have been made smaller and less weighted. Particularly, as a method for manufacturing cylindrical electro-photographic photo-sensitive members of smaller diameters, Japanese Non-examined Patent Publications H05-88385 and H06-262113 disclose methods of simultaneously dipping a plurality of cylindrical base members into a coating liquid and pulling them up at the same time. This simultaneous multi-cylinder dipping method has been widely used judging from the point of improvement of productivity. This method becomes more effective and increases the productivity when the cylindrical base member are closely arranged. In this case, solvent vapor evaporating from the coated films on the substrata and from the surface of the coating liquid in the bath when the substrata are pulled up will make the film dry-up speeds different among cylindrical base member or among surface areas of respective cylindrical base member. This will make film thickness uneven on the substrata. To prevent this, Japanese Non-examined Patent Publications 59-127049 discloses a method comprising the steps of feeding air from the outside to the liquid container and its vicinity to reduce the concentration of solvent vapor near the liquid container before the cylindrical base member are pulled up and drying up the films faster. Further, Japanese Non-examined Patent Publication H03-000151 discloses a method of providing ports for exhausting solvent vapor near the liquid container, connecting these ports to a forced exhaust apparatus having an ON/OFF mechanism, controlling the concentration of solvent vapor near the cylindrical base member while the substrata are pulled up, and thus suppressing unevenness of film thickness.
However, the above technologies are not effective to make the concentration of the solvent vapor uniform near the air supply ports and near the ports for exhausting solvent vapor because the concentration of solvent vapor is smaller near the air supply ports and near the vapor exhausting ports connected to the forced exhaust apparatus but higher away from them.
In other words, the conventional technologies are not satisfactory to solve the above problem that the solvent vapor concentration is uneven near cylindrical base member in the dip-coating. In the conventional technologies, solvent vapor densities are different on the coated surfaces of the cylindrical base member. These uneven vapor densities are apt to cause uneven dry-up speeds and finally uneven thickness of coated layers.
Particularly, in dip coating by the apparatus of simultaneously coating a plurality of cylindrical base member, each cylindrical base member has uneven solvent vapor concentration around it and different dry-up speed. Consequently, each base member has an uneven layer thickness and a leading thin coat area. This also causes reduction in productivity.
To prevent the above-mentioned uneven solvent vapor densities, Japanese Non-examined Patent Publication H08-220786 discloses a method of uniforming the solvent vapor densities over the coating liquid surface by providing vapor exhausting ports in the recycle tube and below the coating liquid level and using a solvent whose specific gravity is greater than that of air and whose saturated vapor concentration is comparatively low. However, this method using solvent of low saturated vapor concentration is slow in drying up the coated layers. Accordingly, the coated layer is apt to move down before the coated layer is dried up to be non sticky to fingers. Consequently, each cylindrical base member has a thinner coated film on the top of the cylinder and a thicker coated film on the bottom of the cylinder. This results in the uneven layer thickness. This uneven layer thickness is apt to occur in a thin coated layer such as a charge generation layer and so on.